The present invention relates to a novel technique for improving the getter efficiency of calcium compounds in removing sulfur from coal.
A large number of small industrial boilers, originally designed for stoker coal, are now operated on gas and oil. While these fuels are more expensive, they offer advantages of ease of handling, cleanliness of operations, and low levels of stack gas emissions. However, due to increasingly limited availability of these fuels, the market for coal has once again expanded. The EPA and industrial requirements demand a method of burning moderate to high sulfur coal efficiently while limiting stack emissions of particulates and SO.sub.2 to the prescribed levels. Current technology gives several alternatives which permit the use of high sulfur coal.
For example, stack gas scrubbing, involving the passing of combustion products through beds of solid sorbants or through solutions of calcium, sodium and/or magnesium, are quite effective at removing SO.sub.2 and particulates. However, their high initial cost coupled with fouling tendencies makes this option unattractive to all but the larger utilities.
Dry injection of limestone into stack gas is a rather ineffective method for controlling sulfur emissions. The formation of an impervious CaSO.sub.4 crust around the limestone particles renders the interior virtually useless for sulfur control purposes. Consequently, only 25% to 40% of the calcium injected is actually reacted. Furthermore, excessive amounts of particulates and ash are generated.
Dry injection of limestone into a pulverized coal bed has the same limitations as the previous technique. While small amounts of sulfur can be economically removed, the vast excess of limestone required negates the use of this method for the combustion of high sulfur coal.
Bricketing or pan-balling mixtures of coal, limestone and optionally a binder such as starch have also been suggested. However, sulfur capture has been found to be very low in these techniques as well.
Accordingly, it is an object of the present invention to provide a new technique for reducing the sulfur emissions produced by the burning of sulfur-containing coal. In addition, it is another object of the present invention to provide a new coal-containing material made from sulfur-containing coal which when burned emits very small amounts of objectionable sulfur-containing materials such as sulfur dioxide.